selftests/bpf: List newest Clang built-ins needed for some CO-RE selftests

Record which built-ins are optional and needed for some of recent BPF CO-RE
subtests. Document Clang diff that fixed corner-case issue with
__builtin_btf_type_id().

Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200820061411.1755905-4-andriin@fb.com

diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst
index e885d35..66acfcf 100644 (file)
--- a/tools/testing/selftests/bpf/README.rst
+++ b/tools/testing/selftests/bpf/README.rst
@@ -43,3 +43,24 @@ This is due to a llvm BPF backend bug. The fix
   https://reviews.llvm.org/D78466
 has been pushed to llvm 10.x release branch and will be
 available in 10.0.1. The fix is available in llvm 11.0.0 trunk.
+
+BPF CO-RE-based tests and Clang version
+=======================================
+
+A set of selftests use BPF target-specific built-ins, which might require
+bleeding-edge Clang versions (Clang 12 nightly at this time).
+
+Few sub-tests of core_reloc test suit (part of test_progs test runner) require
+the following built-ins, listed with corresponding Clang diffs introducing
+them to Clang/LLVM. These sub-tests are going to be skipped if Clang is too
+old to support them, they shouldn't cause build failures or runtime test
+failures:
+
+  - __builtin_btf_type_id() ([0], [1], [2]);
+  - __builtin_preserve_type_info(), __builtin_preserve_enum_value() ([3], [4]).
+
+  [0] https://reviews.llvm.org/D74572
+  [1] https://reviews.llvm.org/D74668
+  [2] https://reviews.llvm.org/D85174
+  [3] https://reviews.llvm.org/D83878
+  [4] https://reviews.llvm.org/D83242

diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_type_id.c b/tools/testing/selftests/bpf/progs/test_core_reloc_type_id.c
index 23e6e6b..22aba3f 100644 (file)
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_type_id.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_type_id.c
@@ -75,10 +75,12 @@ int test_core_type_id(void *ctx)
 {
        /* We use __builtin_btf_type_id() in this tests, but up until the time
         * __builtin_preserve_type_info() was added it contained a bug that
-        * would make this test fail. The bug was fixed with addition of
+        * would make this test fail. The bug was fixed ([0]) with addition of
         * __builtin_preserve_type_info(), though, so that's what we are using
         * to detect whether this test has to be executed, however strange
         * that might look like.
+        *
+        *   [0] https://reviews.llvm.org/D85174
         */
 #if __has_builtin(__builtin_preserve_type_info)
        struct core_reloc_type_id_output *out = (void *)&data.out;